For apt installations, some dependencies may default to interactive user input, such as tzdata. This can be especially an issue when upgrading dependencies, since existing build configurations may break due to new dependencies.

The fix, therefore, is in all all Dockerfiles to specify the following. Using ARG rather than ENV is preferably since it is only used during the build process, and is not present after the Docker image has been completed.

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get install --assume-yes --no-install-recommends \
    g++-arm-linux-gnueabi \
    libc6-dev-armel-cross && \
    /qemu.sh arm

And in all scripts:

export DEBIAN_FRONTEND=noninteractive

This has been useful when upgrading dependencies, since of the newer versions do actually have issues with interactive console input.